With the improvement in technology of manufacturing thin displays such as liquid crystal displays and reduction in prices, an extensive variety of display devices are currently available. A display device may display high-quality videos played back by a DVD player or moving images produced by computer graphics.
To display image data output from a computer or a DVD player on a display device, there is needed a display controller having the capabilities for converting an image signal into a format compatible with the specification of the display device by converting the horizontal frequency or the vertical frequency of the image signal.
The specification (e.g., frame rate and resolution) of an image signal that can be displayed differs depending on the type of the display device. The display controller converts an image signal in adaption to the specification of a display device to which the signal is output. The rate of the vertical synchronizing signal of the NTSC television system is 59.97 Hz and the rate of the vertical synchronizing signal of the PAL television system is 50 Hz. Therefore, in order to display moving images provided in the NTSC format on a television of the PAL system, the frame rate of the moving images is converted to adapt to the PAL system.
A rendering process assuming the NTSC system intrinsically produces frames of moving images at 59.97 Hz. Displaying the moving images on a display operated at a frequency different from the frequency of the rendering process will cause a problem and the quality of moving images as reproduced suffers.
In this background, a general purpose of the present invention is to provide a rendering process technology for displaying moving images on a display device operated at a synchronization frequency different from the frequency of the rendering process.